VB.NET What is Sender used for?

Question

I'm confused as to the purpose of the sender parameter in Winform controls, for example:

Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load

End Sub

I understand i can verify what sender holds by doing something as so:

If TypeOf sender Is Label Then
 'Execute some code...
End If

But is there a good reason that sender is included in every single control when it generates the sub-routine for me? In other words, i double click on a Form and i get the Private Sub form_load (sender....) and e As System.EventArgs.

What are some common usage of these two parameters? Are they always required?

Answer 1

sender contains the sender of the event, so if you had one method bound to multiple controls, you can distinguish them.

For example, if you had ten buttons and wanted to change their text to "You clicked me!" when you clicked one of them, you could use one separate handler for each one using a different button name each time, but it would be much better to handle all of them at once:

Private Sub Button_Click(sender As Object, e As EventArgs) Handles Button1.Click, Button2.Click, Button3.Click, Button4.Click, Button5.Click, Button6.Click, Button7.Click, Button8.Click, Button9.Click
    DirectCast(sender, Button).Text = "You clicked me!"
End Sub